How to take moment vertically? M2

In M1 you got a moment of 0 if the line of action passed through a point yet in M2 you can take moments about a point O to work out the center of mass of particles lined up vertically. How does one take moments about the x-axis too?

I am having trouble understanding your question.

You always take moments about an axis, not about a point. When you take moments "about a point", you are really taking moments about an axis normal to the plane of the paper.

If you take moments about the x-axis, then you find the perpendicular distance from the axis to the line of action of the force.

I think the issue you may be having is that you think of the forces as acting in the x-y plane. We actually set it up so that the forces act in the direction of the z-axis. In other words, if you have a particle of weight W with Cartesian coordinates (0,k) and you take moments about the x-axis, then the moment of the force is Wk.

What I have attached shows what I am having a problem with as how is it taking moments about the x-axis? Where is the perpendicular distance? And isn't the line of action, where gravity is a acting, is going through the axis so there is no moment. It's so confusing.


Posted from TSR Mobile

See attachment.

I am still slightly confused. I see you rotated but in the initial diagram which is a plane but the force goes right through the x-axis.